Vapor compression refrigeration cycle to perform cooling and heating of fluids by the use of state change of materials such as evaporation and condensation has found widespread use for applications such as an air-conditioner, refrigerator, hot-water supplier, etc. A variety of working fluids which are applied for the vapor compression refrigeration cycle, especially fluorocarbon refrigerants, have been developed and practically used. Among the fluids, HCFC22 (monochlorodifluoromethane) is widely used as a refrigerant in a heating and cooling system for air-conditioning.
However, chlorofluorocarbons were found to be responsible for the destruction of the ozone layer when released into the stratosphere and eventually exert seriously adverse effects on the ecosystem including human on the earth. Then, a worldwide agreement calls for the restriction of use and in the future total abolition thereof. Under these circumstances, there is an urgent demand for developing a new refrigerant which has no or little potential to cause the problem of depleting the ozone layer.
As attempts to make up for insufficient performances of a single component refrigerant by the use of mixed refrigerants, many proposals for using non-azeotropic refrigerant blends have recently been raised (e.g., Japanese Unexamined Patent Publication No. 79288/1989, Japanese Examined Patent Publication No. 55942/1994, and Japanese Unexamined Patent Publication No. 287688/1991).
A non-azeotropic mixture causes a composition change during phase change such as evaporation or condensation, because a component having lower boiling point is likely to be evaporated and a component having higher boiling points is likely to be condensed. This tendency of composition change is pronounced in the case of evaporation, i.e., phase change from liquid to vapor, and the tendency is particularly pronounced in the case where the differences of boiling point between components are large. Therefore, when such a non-azeotropic blend is transferred from one container to another, it is common practice to discharge it from liquid phase so as not to arise the phase change. However, even in the case of discharging a refrigerant blend from liquid phase, phase change as much as a few percent occurs in the case where the difference in a boiling point is large between components. This is caused by decrease of pressure and increase of the gaseous space derived from discharging, resulting in evaporation of low-boiling-point components from liquid phase. The composition change, even of a few percent, causes a significant change in performances of refrigerant, and the change not only results in a decrease in capability and efficiency of the refrigerant, but also adversely affects safety of refrigerants such as flammability.
In particular, when using as a refrigerant a non-azeotropic blend comprising 23% of difluoromethane (thereafter referred to as "HFC32"), 25% of pentafluoroethane (thereafter referred to as "HFC125") and 52% of 1,1,1,2-tetrafluoroethane (thereafter referred to as "HFC134a"), which is considered as the most promising substitute for HCFC22, the composition change thereof caused during transfer of the refrigerant from bomb, a feeding container, to an air-conditioner is a serious problem, since ASHRAE STANDARD (1994) establishes the permissible composition range of HFC32(22-24%), HFC125(23-27%) and HFC134a(50-54%).